Gas-filled syringes are useful for a number of applications such as surgical procedures involving the injection of a gas bubble into a patient's body. For example, a retinal tear can be treated using an intraocular surgical procedure during which a gas such as sulfur hexafluoride (SF.sub.6) or perfluoropropane (C.sub.3 F.sub.8) is injected into the eye for gas tamponage. Carbon dioxide (CO.sub.2) gas can be injected into a blood vessel to facilitate percutaneous angioscopy. Nitric oxide (NO) gas and NO-releasing compounds can also be used to treat a number of medical conditions. For example, NO and NO-releasing compounds can be used for treatment of male impotence, inhibition of DNA synthesis and mitochondrial respiration in tumor cells, and relaxation of vascular smooth muscle for control of hypertension.
Gases used for surgery are often expensive and not available for purchase in ready-to-use form. Currently, gases for surgical procedures are purchased in a pressurized tank. Syringes are filled directly from the tank using a filling line. When a syringe is disconnected from the filling line, the gas in the filling line is released into the atmosphere. Thus, this method of preparing syringes for surgery is disadvantageous because a significant amount of gas is wasted. Due to the busy environment of a hospital, shut-off valves on gas tanks are frequently left open accidentally, causing an even greater amount of gas to be wasted than when gas syringes are being filled.
In addition to the problem of wasting expensive gases, a more serious clinical problem associated with filling syringes from gas tanks is dilution of the gas in the syringe prior to surgery. Syringes are sometimes prepared on the morning of the day they are to be used in surgery. The syringes are then placed in the operating room with other surgical devices until they are needed, which can be several hours later. Experiments have shown that leakage of gas from a syringe over a relatively short period of time can cause clinically significant dilution of the gas dose and therefore increase the risk of surgical complications. For instance, the concentration of sulfur hexafluoride in a plastic syringe has been observed to decrease from 97% at 30 seconds after aspiration to 76% at 60 minutes and 2% at 18 hours past aspiration.